Many heating mat devices are being used to warm up driveways and the like to prevent the accumulation of snow or ice. These heating devices can be divided into two separate categories, the permanently installed ones and the removable ones.
The permanent heating devices, such as described in U.S. Pat. No. 3,818,892 to Von Kohorn and U.S. Pat. No. 4,564,745 to Deschenes, are typically installed underneath the pavement of the pathway at relatively high cost, thereby requiring a huge amount of energy to ensure that some heat reaches the outside surface of the pathway. This causes a large amount of heat loss. Also, they are exposed to high risk of damages due to possible soil movement.
The removable heating devices are typically laid onto the pathway surface and therefore more energy efficient. They either use electrical heating elements, such as described in U.S. Pat. No. 3,806,702 to Spencer, U.S. Pat. No. 4,814,580 to Carageorge and U.S. Pat. No. 5,591,365 to Shields, or fluid heated elements, such as described in U.S. Pat. No. 4,646,818 to Ervin, Jr., U.S. Pat. No. 5,003,157 to Hargrove and U.S. Pat. No. 5,966,502 to Pearce. The latter tends to be very complicated and expensive to manufacture even though they provide a more uniform heat distribution if connected to each other over the outdoor exposed surface.
The heating devices with electrical heating wires are much easier and fairly inexpensive to manufacture. On the other hand, they have the disadvantage of the fact that it is fairly tricky to distribute a proper amount of heat to the outdoor exposed surface by sizing the heating elements since the dissipated power is inversely proportional to the length of the heating elements. The bigger the heating mat device is, the more power is needed thus the shorter the heating wire should be, which is contradictory. This is why most of these electrical heating mats are usually available in only one or a few predetermined sizes that are not suited to fit all sizes and shapes of actual driveways, walkways and the like.